Paracrine interactions play an important role in cellular communication within the testis. The presence of opioid peptides and their receptors in the testis has suggested that this peptide family may function, at least in part, as local regulators of testicular function. The PI has succeeded in identifying multiple testicular cell types that express the gene for the opioid peptide precursor, proenkephalin: spermatogenic cells and Sertoli cells. Proenkephalin-derived peptides therefore may mediate intratesticular actions of somatic as well as male germ cells that are important for the regulation of spermatogenesis. In addition, rat and mouse spermatogenic cells contain a unique 1700-nucleotide form of proenkephalin RNA, not found in somatic cells, that is developmentally regulated. The proenkephalin gene thus serves as a model for the regulation of germ-cell gene expression. The aims of this proposal are: (1) to characterize the cis-acting elements within the proenkephalin gene responsible for its expression and developmental stage-specific regulation in spermatogenic cells: and (2) to characterize the translation products derived from proenkephalin RNA in the different testicular cells in which it is present. The latter experiments will be important for the ultimate elucidation of the functions of testicular proenkephalin-derived peptides.